IGEM/UP/1B Edition 4 (March 2026) changed tightness testing so that permissible pressure drop limits are now based on the Installation Volume (IV) of the pipework — not the meter size as before.

Select the fuel gas for the installation you are testing: Natural Gas, LPG or LPG/Air.

Enter the pressure drop in mbar observed during your 2-minute tightness test. Enter 0 if there was no perceptible movement on the gauge at all.

If there is no perceptible movement, the test passes automatically and no IV calculation is needed.

The IV is the internal volume of all the gas pipework in the installation. You calculate it by adding up the volume of each pipe segment using:

For each pipe run, enter the internal diameter in mm and the length in metres. Add as many segments as needed. The calculator totals them automatically.

• Use internal diameter — not outside diameter
• Common internal diameters: 15mm copper = ~13mm, 22mm copper = ~20mm, 28mm copper = ~26mm
• Include all pipework from the meter outlet to each appliance isolation valve
• Do not include the appliances themselves

• ✅ PASS — drop is within permissible limits. You must still isolate appliances and repeat the test to confirm drop is not from pipework.
• ❌ FAIL — drop exceeds permissible limits. Trace and repair the escape before re-testing.
• ⚠️ IV Required — perceptible movement was detected and IV needs to be entered.

This calculator is a guide only. Always refer to the full IGEM/UP/1B Edition 4 standard. The ISU133 bulletin is available in the Technical Bulletins section of the app.